A single detector for detecting pH value of an object and light emitted from the object is proposed in patent document 1. The detector proposed in patent document 1 has a structure combined with a charge transfer type pH detector and a charge transfer type light detector to detect pH value and light alternately in time sequence. Namely, time of detecting pH value and time of detecting light are a little bit out of synchronization.
For attaining high S/N ratio, it is desirable to accumulate charge in the sensing section of the pH detector. If it is assumed to take 0.1 millisecond to accumulate charge one time, it takes 0.1 second to accumulate charge one hundred times, during which the sensing section is not secured to detect light.
If combined detectors are arranged like a matrix, pH distribution (pH image) and light distribution (light image) of the object can be detected.
The following patent documents 2 and 3 are also referred to as references for the invention.    Patent document 1: Japanese Patent Application Laid-Open (JP-A) No. 11-201775    Patent document 2: JP-A No. 2004-28723    Patent document 3: JP-A No. 2002-98667